The present invention relates to the field of conveyors, and more particularly, to a pan assembly for an armored face conveyor, such as for handling coal in a longwall mining system.
Armored face conveyors are literally the foundation of longwall mining machines. Typically, the conveyor line pan assembly includes a hardened steel deck plate attached to supporting cast steel side members. A plurality of these pans are assembled in end to end relationship to form a complete conveyor system to move the coal along the face being mined.
In addition, the side members support the haulage system for the shearer. A scraper chain extends along the entire conveyor system with spaced flights serving to move the coal along the deck. Clearly, the strength of the conveyor pan assembly of the armored face conveyor and its structural integrity is of a primary concern. Eliminating structural failures in the conveyor system, and thus minimizing down time, is important to assure an efficient longwall mining operation.
The main approach in past designs attempting to increase the life of a conveyor pan is simply the modification of the welded joint between the deck plate and the side members. In the past, the focus has been on attempting to make the longitudinal weld withstand wear at the same rate as the deck plate, since in these designs the scraper chain engages the weld. Because the weld material is not as hard as the deck plate it tends to wear quickly.
Generally speaking, the industry follows the approach of butt welding the lateral edges of the deck plate to a corresponding edge on the side members. Modifications to common butt welding techniques include chamfering the edges and then welding along the top and bottom to form a joint; providing a narrow shoulder to support the edge of the deck plate and apply top and bottom fillet welds; and splitting the side members and welding to top and bottom plates. For example, see the U.S. Pat. Nos. to Berwald, 4,484,677, issued Nov. 27, 1984; Skolik et al. 4,420,075 issued Dec. 13, 1983; and Gehle et al. 4,373,757, issued Feb. 15, 1983; respectively.
While some of these modifications have provided limited improvement, typically the weld bead joining the deck plate to the sides of the conveyor pan assembly is still the governing factor limiting the life of the armored face conveyor pan. As a result, the life of conveyor system is seriously restricted. Elimination of the wear factor of the conveyor pan, as well as simply the improving the overall strength and integrity of the pan is thus desirable.
Furthermore, improvement in the manufacturing efficiency of the pan assembly is desirable. When dealing with welding along the typical butt joints between the deck plate and the side members, it is normally necessary to set up manufacturing jigs to align the two edges being welded. This is a costly and time consuming process, especially in light of the substantial weight of these component parts. Finding a way in which the parts could be self aligning and supporting could represent significant savings in the overall cost of a conveyor system.
It is also recognized in the art that the amount of welding required along the typical butt joint that is subject to scraper chain conveyor wear is excessive. In the past, some effort has been made to reduce the number of welding passes required to form a reasonably strong joint, but these efforts have not resulted in any appreciable success. At least approximately 18 welding passes is standard in the industry in order to ensure reasonable strength and integrity of the joints. A manner in which the welding operation could be reduced would also go a long way in further reducing the original manufacturing cost of these conveyor systems.
Finally, the limited shear strength of the typical butt weld joint for connecting the deck plate to the side members results in failures that are rather frequent, thus adding another cause to deleterious shutdowns of the conveyor system for repairs. Typically, the shear force applied to the joint causes cracking of the weld and eventual failure. A way in which to reduce the shear forces acting on the weld joint would help in further improving the life of the conveyor pan assembly.